llvm dev - Jul 2017 - moving libfuzzer to compiler-rt?

On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov <ekarpenkov at
apple.com>
wrote:
>
> On Jul 12, 2017, at 11:01 AM, Kostya Serebryany <kcc at google.com>
wrote:
> One question: will it make sense to *copy* the code to the new location,
> work on it, then delete the code from the old location,
> instead of doing a move in a single commit?
> I don't expect any dramatic changes in the code structure during a few
> weeks, so 'copy' might be much simpler than 'move’.
>
>
> I am not sure how we would handle CMake targets collision (I think we
> would have one: check-fuzzer vs. check-fuzzer)
> Of course, I can give it a different name for now,
>
Yep. 'check-fuzzer-temporary' or some such.

> but that would potentially add even more confusion and complexity.
>
> Though it seems like a good idea to at least see what would happen to
> buildbots.
>
> I already forgot why we decided not to move the code to compiler-rt.
>
> This would solve at least this problem.
> Since we now have -fsanitize=fuzzer it will actually be pretty natural.
>
>
> Licensing concerns, compiler-rt has a different license.
>
@%##%)*%

But wait a sec, the sanitizers are ok with this license, why libFuzzer
isn't?
(Sorry, my memory has been flushed over the last month)

>
> BTW libFuzzer CMake has a crazy amount of hacks to work under Windows,
> where logic in many parts
> is entirely different, so any help on testing and fixing arising issues
> would be much appreciated.
>
It's totally fine for me if we *copy* the code to the new location and
ditch the windows support completely.
Then, whoever cares about windows, will reinstate it in the new location
once the dust settles.

> All I can do is to make a commit and then try to understand the response
> from a bots,
> which is not very efficient.
>
>
>
>>
>> 3) CMake files in LLVM root repository do a rather large amount of
>> trickery:
>> more warning flags are introduced, default linking commands for
different
>> platforms are changed,
>> etc.
>> None of this is picked up when running from the “runtimes” directory,
>> which is often undesirable,
>> as the runtime would be built very differently from the rest of LLVM,
>> missing those desired warnings/optimizations.
>>
>> Additionally, working with “runtimes” introduces some inherent
>> restrictions.
>> Namely:
>>
>> 4) Extra arguments to CMake will not be propagated.
>> E.g. invoking `cmake … -DLLVM_USE_SANITIZE_COVERAGE=1` will not have
any
>> effect on the compilation of any project
>> in “runtimes”.
>> It’s not clear how those flags can be explicitly propagated.
>>
>> 5) In a similar vein to (4), additional flags to `ninja` will not be
>> propagated.
>> E.g. running “ninja -v check-blah” will actually not show the commands
>> required to execute the tests,
>> as it goes through a CMake invocation.
>> This issue has a workaround: ninja can be launched directly from
>> “runtimes/runtime-bins”, but that is counterintuitive.
>>
>> 6) Recursive invocation required for “runtimes” breaks
>> `compile_commands.json` construction, which is used
>> by many editors and tools (e.g. Vim+Ale or rtags) for go-to-defintion
and
>> error highlight functionality.
>> There is a workaround: a separate `compile_commands.json` is generated
>> for the `runtimes` directory,
>> and it might be possible to write some magic to inject it back into the
>> parent one, but that would be yet-another-piece-of-build-infrastructure
>> which would have to be maintained.
>>
>> 7) Similarly to (6), recursive invocation breaks XCode tooling: in a
>> generated XCode project,
>> no libfuzzer files are accessible. I would assume same would hold for
>> other IDEs.
>>
>> Any thoughts or comments on these?
>> While (1) is not really a problem, and I can probably find a workaround
>> for (2), the issues
>> listed in (3)-(7) seem inherent to recursive CMake invocation.
>> I can think of a number of alternative suggestions, which would solve
the
>> problem of requiring a 2-stage build:
>>
>> a) We can move the compilation commands for libFuzzer tests from CMake
>> into lit.
>> This would have an added benefit of each lit test being self-contained:
>> it would be sufficient to just run
>> “lit” to reproduce everything, and it would pick up all changes to
>> compiler/coverage instrumentation/sanitizers/etc.
>> The first run would generate the tested binaries, and further tinkering
>> could be done with binaries directly if desired.
>>
>> b) We can use the “tools” directory instead.
>>
>>
>> Thanks,
>> George
>>
>> On May 11, 2017, at 10:31 AM, Kostya Serebryany <kcc at
google.com> wrote:
>>
>>
>>
>> On Wed, May 10, 2017 at 6:09 PM, Chris Bieneman via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>>
>>> On May 10, 2017, at 4:43 PM, George Karpenkov via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> Actually, there’s another problem we have missed: libraries under
>>> `build/lib` are not installed into toolchain
>>> on mac os (and neither on linux, I would suppose).
>>>
>>>
>>> Actually that isn't accurate. By default we don't install
the LLVM
>>> libraries, but that is completely configurable in the build system.
It
>>> doesn't work for libFuzzer because the CMake build for
libFuzzer is not
>>> built using any of the LLVM CMake modules or following any of
LLVM's
>>> conventions.
>>>
>>> Thus installations of Clang would not contain libLLVMFuzzer, but we
>>> would like them to, so that users would not have
>>> to compile anything, and could just call `clang -fsanitize=fuzzer`.
>>>
>>> That could probably be done with another CMake change, but I have
no
>>> idea how to do that.
>>>
>>>
>>> Yea, libFuzzer's CMake really needs a big overhaul, and
probably an
>>> almost complete rewrite.
>>>
>>
>> no objections.
>>
>>
>>>
>>> -Chris
>>>
>>>
>>> On May 9, 2017, at 4:04 PM, George Karpenkov via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>
>>> On May 9, 2017, at 3:00 PM, Kostya Serebryany <kcc at
google.com> wrote:
>>>
>>> Thanks for the explanations! (it was worth asking)
>>>
>>> I do want to build libFuzzer itself (and its tests) using the
just-built
>>> clang. So, llvm/runtimes then.
>>> I'd name the directory llvm/runtimes/libFuzzer, if possible
(the old
>>> path was lib/Fuzzer which is how the tool got it's name,
actually)
>>> George, would you like to send the change for review?
>>>
>>> OK
>>>
>>>
>>> --kcc
>>>
>>>
>>>
>>> On Tue, May 9, 2017 at 2:37 PM, Chris Bieneman <cbieneman at
apple.com>
>>> wrote:
>>>
>>>>
>>>> On May 9, 2017, at 2:19 PM, George Karpenkov <ekarpenkov at
apple.com>
>>>> wrote:
>>>>
>>>> +Chris.
>>>>
>>>> My understanding was that it is technically impossible for
things in
>>>> “lib”, as they are built first, and there’s no way to tell them
to do that
>>>> before “clang”.
>>>> I’m not a CMake expert, and I might be wrong.
>>>>
>>>>
>>>> It is not impossible, it would just involve excessive hacks.
Since it
>>>> seems like this isn't a short-term solution we're
talking about I am very
>>>> opposed to throwing hacks into the build system. I'd rather
we actually fix
>>>> the problem(s). More below.
>>>>
>>>>
>>>> On May 9, 2017, at 2:15 PM, Kostya Serebryany <kcc at
google.com> wrote:
>>>>
>>>>
>>>>
>>>> On Tue, May 9, 2017 at 1:56 PM, George Karpenkov <ekarpenkov
at apple.com>
>>>>  wrote:
>>>>
>>>>> Again, after offline conversation with Chris Bieneman:
>>>>>
>>>>>  - move to compiler-rt would be too complicated due to
change in
>>>>> licenses
>>>>>  - it would make much more sense to move to “tools” folder
instead,
>>>>> for the following reasons:
>>>>>     * conceptually, it’s a tool, not a library
>>>>>     * all other projects in “lib” depend on LLVM and can
not build
>>>>> without LLVM, libFuzzer does not
>>>>>     * practically speaking, CMake has no way of knowing
whether Clang
>>>>> is being built when
>>>>>       “lib” is compiled, yet it does know for projects in
tools.
>>>>>
>>>>> Using a freshly built clang for projects in “tools” is
embarrassingly
>>>>> easy and only requires a couple of lines
>>>>> of configuration change.
>>>>>
>>>>> Kostya, what about moving to “tools” then?
>>>>>
>>>>
>>>> Well, ok, this sounds cool.
>>>> But can we make one more step and try to preserve the code
where it is,
>>>> for the sake of compatibility?
>>>>
>>>>
>>>> Please no. This code doesn't actually belong in lib, it has
never fit
>>>> the model of an LLVM library, we really need to pull it out of
there.
>>>>
>>>> E.g. can we have the CMake in tools while still keeping the
code in
>>>> lib?
>>>>
>>>>
>>>> Could we contrive a hack in the build system to do it? Yes, but
I will
>>>> fight violently against allowing that change into the build
system because
>>>> the right answer here is to move the code.
>>>>
>>>> Or a link of some kind?
>>>>
>>>>
>>>> Links are incredibly fragile on Windows, and they trip up a lot
of SCM
>>>> tools. We have one in LLDB's repo that causes me nothing
but problems, so I
>>>> am also strongly opposed to that.
>>>>
>>>>
>>>> My worry is that there are already quite a few places that know
where
>>>> libFuzzer code is,
>>>> and I don't control all of them.
>>>>
>>>>
>>>> Downstream clients will have to update. That is kinda how these
things
>>>> work, I can't imagine re-pointing an SCM checkout being a
huge burden.
>>>>
>>>>
>>>> And, finally, I really don't get why we can do something in
tools and
>>>> can't do the same in lib.
>>>> Or we simply don't want to do it to keep things simple?
>>>>
>>>>
>>>> Not all functionality in CMake is order-independent.
Specifically the
>>>> detection of targets is not. In order to support what
you're trying to do
>>>> you are going to change behavior based on the presence of the
clang target.
>>>> Which means the clang target must be added before your CMake is
processed.
>>>>
>>>> To support this our build system has strict ordering
requirements such
>>>> that things in lib cannot depend on things in tools. If you
need to depend
>>>> on clang, you need to not be in lib.
>>>>
>>>> Also, generally speaking Fuzzer is a library under lib that
also has
>>>> nested tests, which is *not* how the lib directory is supposed
to be
>>>> structured. It never should have been allowed to be structured
like that.
>>>> If you want the tests next to the library, it is a tool or a
runtime, but
>>>> not a lib.
>>>>
>>>> As I see there are two options to move forward with, and it
really
>>>> depends on how you intend to use the just-built clang.
>>>>
>>>> (1) If you want to use just-built clang to build libFuzzer and
its
>>>> tests, it should be a runtime.
>>>> (2) If you want to use just-built clang to only build
libFuzzer's
>>>> tests, it should be a tool.
>>>>
>>>> I think that since it is a runtime library, it should be a
runtime, and
>>>> I expect it would mostly work to just copy the Fuzzer directory
into
>>>> llvm/runtimes.
>>>>
>>>> -Chris
>>>>
>>>>
>>>> --kcc
>>>>
>>>>
>>>>
>>>>>
>>>>> On May 9, 2017, at 11:07 AM, Dan Liew <dan at
su-root.co.uk> wrote:
>>>>>
>>>>> On 9 May 2017 at 18:55, Kostya Serebryany <kcc at
google.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On Tue, May 9, 2017 at 10:23 AM, Dan Liew <dan at
su-root.co.uk> wrote:
>>>>>
>>>>>
>>>>> Does anyone see good reasons why libFuzzer should remain in
llvm repo
>>>>> (as
>>>>> opposed to moving it to compiler-rt)?
>>>>>
>>>>>
>>>>> Does moving LibFuzzer to compiler-rt imply that it is
compiled as part
>>>>> of compiler-rt and shipped with it?
>>>>>
>>>>> How does that fit with LibFuzzer's model of allowing
the user to
>>>>> provide their own `main()`.
>>>>>
>>>>>
>>>>>
>>>>> libFuzzer doesn't allow users to use their own main
(not any more).
>>>>> Although I am not sure how that's related to moving
libFuzzer
>>>>> somewhere.
>>>>>
>>>>>
>>>>> Oops. That shows how long it's been since I looked at
the source code.
>>>>>
>>>>> It was related in that if LibFuzzer was shipped as part of
compiler-rt
>>>>> I presumed we would need to supply both libraries to end
users.
>>>>> Given that this feature was removed it is a non-issue.
>>>>>
>>>>>
>>>>
>>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
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> On Jul 12, 2017, at 11:34 AM, Kostya Serebryany <kcc at google.com>
wrote:
> 
> 
> 
> On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov <ekarpenkov at
apple.com <mailto:ekarpenkov at apple.com>> wrote:
> 
>> On Jul 12, 2017, at 11:01 AM, Kostya Serebryany <kcc at google.com
<mailto:kcc at google.com>> wrote:
>> One question: will it make sense to *copy* the code to the new
location, work on it, then delete the code from the old location,
>> instead of doing a move in a single commit? 
>> I don't expect any dramatic changes in the code structure during a
few weeks, so 'copy' might be much simpler than 'move’.
> 
> I am not sure how we would handle CMake targets collision (I think we would
have one: check-fuzzer vs. check-fuzzer)
> Of course, I can give it a different name for now,
> 
> Yep. 'check-fuzzer-temporary' or some such. 
>  
> but that would potentially add even more confusion and complexity.
> 
> Though it seems like a good idea to at least see what would happen to
buildbots.
> 
>> I already forgot why we decided not to move the code to compiler-rt. 
> 
>> This would solve at least this problem. 
>> Since we now have -fsanitize=fuzzer it will actually be pretty natural.
> 
> Licensing concerns, compiler-rt has a different license.
> 
> @%##%)*%
> 
> But wait a sec, the sanitizers are ok with this license, why libFuzzer
isn't?
> (Sorry, my memory has been flushed over the last month)
Apparently because the code was already contributed under a different license.
IANAL but apparently to do the change in a fully correct way one would need to
chase
down every single contributor and ask them to agree to a license change.
>  
> 
> BTW libFuzzer CMake has a crazy amount of hacks to work under Windows,
where logic in many parts
> is entirely different, so any help on testing and fixing arising issues
would be much appreciated.
> 
> It's totally fine for me if we *copy* the code to the new location and
ditch the windows support completely.
> Then, whoever cares about windows, will reinstate it in the new location
once the dust settles.
>  
> All I can do is to make a commit and then try to understand the response
from a bots,
> which is not very efficient.
> 
>>  
>> 
>> 3) CMake files in LLVM root repository do a rather large amount of
trickery:
>> more warning flags are introduced, default linking commands for
different platforms are changed,
>> etc.
>> None of this is picked up when running from the “runtimes” directory,
which is often undesirable,
>> as the runtime would be built very differently from the rest of LLVM,
missing those desired warnings/optimizations.
>> 
>> Additionally, working with “runtimes” introduces some inherent
restrictions.
>> Namely:
>> 
>> 4) Extra arguments to CMake will not be propagated.
>> E.g. invoking `cmake … -DLLVM_USE_SANITIZE_COVERAGE=1` will not have
any effect on the compilation of any project
>> in “runtimes”.
>> It’s not clear how those flags can be explicitly propagated.
>> 
>> 5) In a similar vein to (4), additional flags to `ninja` will not be
propagated.
>> E.g. running “ninja -v check-blah” will actually not show the commands
required to execute the tests,
>> as it goes through a CMake invocation.
>> This issue has a workaround: ninja can be launched directly from
“runtimes/runtime-bins”, but that is counterintuitive.
>> 
>> 6) Recursive invocation required for “runtimes” breaks
`compile_commands.json` construction, which is used
>> by many editors and tools (e.g. Vim+Ale or rtags) for go-to-defintion
and error highlight functionality.
>> There is a workaround: a separate `compile_commands.json` is generated
for the `runtimes` directory,
>> and it might be possible to write some magic to inject it back into the
parent one, but that would be yet-another-piece-of-build-infrastructure
>> which would have to be maintained.
>> 
>> 7) Similarly to (6), recursive invocation breaks XCode tooling: in a
generated XCode project,
>> no libfuzzer files are accessible. I would assume same would hold for
other IDEs.
>> 
>> Any thoughts or comments on these?
>> While (1) is not really a problem, and I can probably find a workaround
for (2), the issues
>> listed in (3)-(7) seem inherent to recursive CMake invocation.
>> I can think of a number of alternative suggestions, which would solve
the problem of requiring a 2-stage build:
>> 
>> a) We can move the compilation commands for libFuzzer tests from CMake
into lit.
>> This would have an added benefit of each lit test being self-contained:
it would be sufficient to just run
>> “lit” to reproduce everything, and it would pick up all changes to
compiler/coverage instrumentation/sanitizers/etc.
>> The first run would generate the tested binaries, and further tinkering
could be done with binaries directly if desired.
>> 
>> b) We can use the “tools” directory instead.
>> 
>> 
>> Thanks,
>> George
>> 
>>> On May 11, 2017, at 10:31 AM, Kostya Serebryany <kcc at
google.com <mailto:kcc at google.com>> wrote:
>>> 
>>> 
>>> 
>>> On Wed, May 10, 2017 at 6:09 PM, Chris Bieneman via llvm-dev
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
>>> 
>>>> On May 10, 2017, at 4:43 PM, George Karpenkov via llvm-dev
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
>>>> 
>>>> Actually, there’s another problem we have missed: libraries
under `build/lib` are not installed into toolchain
>>>> on mac os (and neither on linux, I would suppose).
>>> 
>>> Actually that isn't accurate. By default we don't install
the LLVM libraries, but that is completely configurable in the build system. It
doesn't work for libFuzzer because the CMake build for libFuzzer is not
built using any of the LLVM CMake modules or following any of LLVM's
conventions.
>>> 
>>>> Thus installations of Clang would not contain libLLVMFuzzer,
but we would like them to, so that users would not have
>>>> to compile anything, and could just call `clang
-fsanitize=fuzzer`.
>>>> 
>>>> That could probably be done with another CMake change, but I
have no idea how to do that.
>>> 
>>> Yea, libFuzzer's CMake really needs a big overhaul, and
probably an almost complete rewrite.
>>> 
>>> no objections.
>>>  
>>> 
>>> -Chris
>>> 
>>>> 
>>>>> On May 9, 2017, at 4:04 PM, George Karpenkov via llvm-dev
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
>>>>> 
>>>>>> 
>>>>>> On May 9, 2017, at 3:00 PM, Kostya Serebryany <kcc
at google.com <mailto:kcc at google.com>> wrote:
>>>>>> 
>>>>>> Thanks for the explanations! (it was worth asking) 
>>>>>> 
>>>>>> I do want to build libFuzzer itself (and its tests)
using the just-built clang. So, llvm/runtimes then.
>>>>>> I'd name the directory llvm/runtimes/libFuzzer, if
possible (the old path was lib/Fuzzer which is how the tool got it's name,
actually)
>>>>>> George, would you like to send the change for review? 
>>>>> OK
>>>>>> 
>>>>>> --kcc
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> On Tue, May 9, 2017 at 2:37 PM, Chris Bieneman
<cbieneman at apple.com <mailto:cbieneman at apple.com>> wrote:
>>>>>> 
>>>>>>> On May 9, 2017, at 2:19 PM, George Karpenkov
<ekarpenkov at apple.com <mailto:ekarpenkov at apple.com>> wrote:
>>>>>>> 
>>>>>>> +Chris.
>>>>>>> 
>>>>>>> My understanding was that it is technically
impossible for things in “lib”, as they are built first, and there’s no way to
tell them to do that before “clang”.
>>>>>>> I’m not a CMake expert, and I might be wrong.
>>>>>> 
>>>>>> It is not impossible, it would just involve excessive
hacks. Since it seems like this isn't a short-term solution we're
talking about I am very opposed to throwing hacks into the build system. I'd
rather we actually fix the problem(s). More below.
>>>>>> 
>>>>>>> 
>>>>>>>> On May 9, 2017, at 2:15 PM, Kostya Serebryany
<kcc at google.com <mailto:kcc at google.com>> wrote:
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> On Tue, May 9, 2017 at 1:56 PM, George
Karpenkov <ekarpenkov at apple.com <mailto:ekarpenkov at apple.com>>
wrote:
>>>>>>>> Again, after offline conversation with Chris
Bieneman:
>>>>>>>> 
>>>>>>>>  - move to compiler-rt would be too complicated
due to change in licenses
>>>>>>>>  - it would make much more sense to move to
“tools” folder instead, for the following reasons:
>>>>>>>>     * conceptually, it’s a tool, not a library
>>>>>>>>     * all other projects in “lib” depend on
LLVM and can not build without LLVM, libFuzzer does not
>>>>>>>>     * practically speaking, CMake has no way of
knowing whether Clang is being built when
>>>>>>>>       “lib” is compiled, yet it does know for
projects in tools.
>>>>>>>> 
>>>>>>>> Using a freshly built clang for projects in
“tools” is embarrassingly easy and only requires a couple of lines
>>>>>>>> of configuration change.
>>>>>>>> 
>>>>>>>> Kostya, what about moving to “tools” then?
>>>>>>>> 
>>>>>>>> Well, ok, this sounds cool. 
>>>>>>>> But can we make one more step and try to
preserve the code where it is, for the sake of compatibility?
>>>>>> 
>>>>>> Please no. This code doesn't actually belong in
lib, it has never fit the model of an LLVM library, we really need to pull it
out of there.
>>>>>> 
>>>>>>>> E.g. can we have the CMake in tools while still
keeping the code in lib?
>>>>>> 
>>>>>> Could we contrive a hack in the build system to do it?
Yes, but I will fight violently against allowing that change into the build
system because the right answer here is to move the code.
>>>>>> 
>>>>>>>> Or a link of some kind?
>>>>>> 
>>>>>> Links are incredibly fragile on Windows, and they trip
up a lot of SCM tools. We have one in LLDB's repo that causes me nothing but
problems, so I am also strongly opposed to that.
>>>>>> 
>>>>>>>> 
>>>>>>>> My worry is that there are already quite a few
places that know where libFuzzer code is,
>>>>>>>> and I don't control all of them. 
>>>>>> 
>>>>>> Downstream clients will have to update. That is kinda
how these things work, I can't imagine re-pointing an SCM checkout being a
huge burden.
>>>>>> 
>>>>>>>> 
>>>>>>>> And, finally, I really don't get why we can
do something in tools and can't do the same in lib.
>>>>>>>> Or we simply don't want to do it to keep
things simple?
>>>>>> 
>>>>>> Not all functionality in CMake is order-independent.
Specifically the detection of targets is not. In order to support what
you're trying to do you are going to change behavior based on the presence
of the clang target. Which means the clang target must be added before your
CMake is processed.
>>>>>> 
>>>>>> To support this our build system has strict ordering
requirements such that things in lib cannot depend on things in tools. If you
need to depend on clang, you need to not be in lib.
>>>>>> 
>>>>>> Also, generally speaking Fuzzer is a library under lib
that also has nested tests, which is *not* how the lib directory is supposed to
be structured. It never should have been allowed to be structured like that. If
you want the tests next to the library, it is a tool or a runtime, but not a
lib.
>>>>>> 
>>>>>> As I see there are two options to move forward with,
and it really depends on how you intend to use the just-built clang.
>>>>>> 
>>>>>> (1) If you want to use just-built clang to build
libFuzzer and its tests, it should be a runtime.
>>>>>> (2) If you want to use just-built clang to only build
libFuzzer's tests, it should be a tool.
>>>>>> 
>>>>>> I think that since it is a runtime library, it should
be a runtime, and I expect it would mostly work to just copy the Fuzzer
directory into llvm/runtimes.
>>>>>> 
>>>>>> -Chris
>>>>>> 
>>>>>>>> 
>>>>>>>> --kcc 
>>>>>>>> 
>>>>>>>>  
>>>>>>>> 
>>>>>>>>> On May 9, 2017, at 11:07 AM, Dan Liew
<dan at su-root.co.uk <mailto:dan at su-root.co.uk>> wrote:
>>>>>>>>> 
>>>>>>>>> On 9 May 2017 at 18:55, Kostya Serebryany
<kcc at google.com <mailto:kcc at google.com>> wrote:
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> On Tue, May 9, 2017 at 10:23 AM, Dan
Liew <dan at su-root.co.uk <mailto:dan at su-root.co.uk>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>>> Does anyone see good reasons
why libFuzzer should remain in llvm repo
>>>>>>>>>>>> (as
>>>>>>>>>>>> opposed to moving it to
compiler-rt)?
>>>>>>>>>>> 
>>>>>>>>>>> Does moving LibFuzzer to
compiler-rt imply that it is compiled as part
>>>>>>>>>>> of compiler-rt and shipped with it?
>>>>>>>>>>> 
>>>>>>>>>>> How does that fit with
LibFuzzer's model of allowing the user to
>>>>>>>>>>> provide their own `main()`.
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> libFuzzer doesn't allow users to
use their own main (not any more).
>>>>>>>>>> Although I am not sure how that's
related to moving libFuzzer somewhere.
>>>>>>>>> 
>>>>>>>>> Oops. That shows how long it's been
since I looked at the source code.
>>>>>>>>> 
>>>>>>>>> It was related in that if LibFuzzer was
shipped as part of compiler-rt
>>>>>>>>> I presumed we would need to supply both
libraries to end users.
>>>>>>>>> Given that this feature was removed it is a
non-issue.
>>>>>>> 
>>>>>> 
>>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>>> 
>>> 
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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On Wed, Jul 12, 2017 at 11:54 AM, George Karpenkov <ekarpenkov at
apple.com>
wrote:
>
> On Jul 12, 2017, at 11:34 AM, Kostya Serebryany <kcc at google.com>
wrote:
>
>
>
> On Wed, Jul 12, 2017 at 11:30 AM, George Karpenkov <ekarpenkov at
apple.com>
> wrote:
>
>>
>> On Jul 12, 2017, at 11:01 AM, Kostya Serebryany <kcc at
google.com> wrote:
>> One question: will it make sense to *copy* the code to the new
location,
>> work on it, then delete the code from the old location,
>> instead of doing a move in a single commit?
>> I don't expect any dramatic changes in the code structure during a
few
>> weeks, so 'copy' might be much simpler than 'move’.
>>
>>
>> I am not sure how we would handle CMake targets collision (I think we
>> would have one: check-fuzzer vs. check-fuzzer)
>> Of course, I can give it a different name for now,
>>
>
> Yep. 'check-fuzzer-temporary' or some such.
>
>
>> but that would potentially add even more confusion and complexity.
>>
>> Though it seems like a good idea to at least see what would happen to
>> buildbots.
>>
>> I already forgot why we decided not to move the code to compiler-rt.
>>
>> This would solve at least this problem.
>> Since we now have -fsanitize=fuzzer it will actually be pretty natural.
>>
>>
>> Licensing concerns, compiler-rt has a different license.
>>
>
> @%##%)*%
>
> But wait a sec, the sanitizers are ok with this license, why libFuzzer
> isn't?
> (Sorry, my memory has been flushed over the last month)
>
>
> Apparently because the code was already contributed under a different
> license.
> IANAL but apparently to do the change in a fully correct way one would
> need to chase
> down every single contributor and ask them to agree to a license change.
>
This is a PITA, but we should do it.
licensing issues like this should not prevent us from making our own code
better.


>
>
>
>>
>> BTW libFuzzer CMake has a crazy amount of hacks to work under Windows,
>> where logic in many parts
>> is entirely different, so any help on testing and fixing arising issues
>> would be much appreciated.
>>
>
> It's totally fine for me if we *copy* the code to the new location and
> ditch the windows support completely.
> Then, whoever cares about windows, will reinstate it in the new location
> once the dust settles.
>
>
>
>> All I can do is to make a commit and then try to understand the
response
>> from a bots,
>> which is not very efficient.
>>
>>
>>
>>>
>>> 3) CMake files in LLVM root repository do a rather large amount of
>>> trickery:
>>> more warning flags are introduced, default linking commands for
>>> different platforms are changed,
>>> etc.
>>> None of this is picked up when running from the “runtimes”
directory,
>>> which is often undesirable,
>>> as the runtime would be built very differently from the rest of
LLVM,
>>> missing those desired warnings/optimizations.
>>>
>>> Additionally, working with “runtimes” introduces some inherent
>>> restrictions.
>>> Namely:
>>>
>>> 4) Extra arguments to CMake will not be propagated.
>>> E.g. invoking `cmake … -DLLVM_USE_SANITIZE_COVERAGE=1` will not
have
>>> any effect on the compilation of any project
>>> in “runtimes”.
>>> It’s not clear how those flags can be explicitly propagated.
>>>
>>> 5) In a similar vein to (4), additional flags to `ninja` will not
be
>>> propagated.
>>> E.g. running “ninja -v check-blah” will actually not show the
commands
>>> required to execute the tests,
>>> as it goes through a CMake invocation.
>>> This issue has a workaround: ninja can be launched directly from
>>> “runtimes/runtime-bins”, but that is counterintuitive.
>>>
>>> 6) Recursive invocation required for “runtimes” breaks
>>> `compile_commands.json` construction, which is used
>>> by many editors and tools (e.g. Vim+Ale or rtags) for
go-to-defintion
>>> and error highlight functionality.
>>> There is a workaround: a separate `compile_commands.json` is
generated
>>> for the `runtimes` directory,
>>> and it might be possible to write some magic to inject it back into
the
>>> parent one, but that would be
yet-another-piece-of-build-infrastructure
>>> which would have to be maintained.
>>>
>>> 7) Similarly to (6), recursive invocation breaks XCode tooling: in
a
>>> generated XCode project,
>>> no libfuzzer files are accessible. I would assume same would hold
for
>>> other IDEs.
>>>
>>> Any thoughts or comments on these?
>>> While (1) is not really a problem, and I can probably find a
workaround
>>> for (2), the issues
>>> listed in (3)-(7) seem inherent to recursive CMake invocation.
>>> I can think of a number of alternative suggestions, which would
solve
>>> the problem of requiring a 2-stage build:
>>>
>>> a) We can move the compilation commands for libFuzzer tests from
CMake
>>> into lit.
>>> This would have an added benefit of each lit test being
self-contained:
>>> it would be sufficient to just run
>>> “lit” to reproduce everything, and it would pick up all changes to
>>> compiler/coverage instrumentation/sanitizers/etc.
>>> The first run would generate the tested binaries, and further
tinkering
>>> could be done with binaries directly if desired.
>>>
>>> b) We can use the “tools” directory instead.
>>>
>>>
>>> Thanks,
>>> George
>>>
>>> On May 11, 2017, at 10:31 AM, Kostya Serebryany <kcc at
google.com> wrote:
>>>
>>>
>>>
>>> On Wed, May 10, 2017 at 6:09 PM, Chris Bieneman via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>>
>>>> On May 10, 2017, at 4:43 PM, George Karpenkov via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>> Actually, there’s another problem we have missed: libraries
under
>>>> `build/lib` are not installed into toolchain
>>>> on mac os (and neither on linux, I would suppose).
>>>>
>>>>
>>>> Actually that isn't accurate. By default we don't
install the LLVM
>>>> libraries, but that is completely configurable in the build
system. It
>>>> doesn't work for libFuzzer because the CMake build for
libFuzzer is not
>>>> built using any of the LLVM CMake modules or following any of
LLVM's
>>>> conventions.
>>>>
>>>> Thus installations of Clang would not contain libLLVMFuzzer,
but we
>>>> would like them to, so that users would not have
>>>> to compile anything, and could just call `clang
-fsanitize=fuzzer`.
>>>>
>>>> That could probably be done with another CMake change, but I
have no
>>>> idea how to do that.
>>>>
>>>>
>>>> Yea, libFuzzer's CMake really needs a big overhaul, and
probably an
>>>> almost complete rewrite.
>>>>
>>>
>>> no objections.
>>>
>>>
>>>>
>>>> -Chris
>>>>
>>>>
>>>> On May 9, 2017, at 4:04 PM, George Karpenkov via llvm-dev <
>>>> llvm-dev at lists.llvm.org> wrote:
>>>>
>>>>
>>>> On May 9, 2017, at 3:00 PM, Kostya Serebryany <kcc at
google.com> wrote:
>>>>
>>>> Thanks for the explanations! (it was worth asking)
>>>>
>>>> I do want to build libFuzzer itself (and its tests) using the
just-built
>>>> clang. So, llvm/runtimes then.
>>>> I'd name the directory llvm/runtimes/libFuzzer, if possible
(the old
>>>> path was lib/Fuzzer which is how the tool got it's name,
actually)
>>>> George, would you like to send the change for review?
>>>>
>>>> OK
>>>>
>>>>
>>>> --kcc
>>>>
>>>>
>>>>
>>>> On Tue, May 9, 2017 at 2:37 PM, Chris Bieneman <cbieneman at
apple.com>
>>>> wrote:
>>>>
>>>>>
>>>>> On May 9, 2017, at 2:19 PM, George Karpenkov <ekarpenkov
at apple.com>
>>>>> wrote:
>>>>>
>>>>> +Chris.
>>>>>
>>>>> My understanding was that it is technically impossible for
things in
>>>>> “lib”, as they are built first, and there’s no way to tell
them to do that
>>>>> before “clang”.
>>>>> I’m not a CMake expert, and I might be wrong.
>>>>>
>>>>>
>>>>> It is not impossible, it would just involve excessive
hacks. Since it
>>>>> seems like this isn't a short-term solution we're
talking about I am very
>>>>> opposed to throwing hacks into the build system. I'd
rather we actually fix
>>>>> the problem(s). More below.
>>>>>
>>>>>
>>>>> On May 9, 2017, at 2:15 PM, Kostya Serebryany <kcc at
google.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On Tue, May 9, 2017 at 1:56 PM, George Karpenkov
<ekarpenkov at apple.com
>>>>> > wrote:
>>>>>
>>>>>> Again, after offline conversation with Chris Bieneman:
>>>>>>
>>>>>>  - move to compiler-rt would be too complicated due to
change in
>>>>>> licenses
>>>>>>  - it would make much more sense to move to “tools”
folder instead,
>>>>>> for the following reasons:
>>>>>>     * conceptually, it’s a tool, not a library
>>>>>>     * all other projects in “lib” depend on LLVM and
can not build
>>>>>> without LLVM, libFuzzer does not
>>>>>>     * practically speaking, CMake has no way of knowing
whether
>>>>>> Clang is being built when
>>>>>>       “lib” is compiled, yet it does know for projects
in tools.
>>>>>>
>>>>>> Using a freshly built clang for projects in “tools” is
embarrassingly
>>>>>> easy and only requires a couple of lines
>>>>>> of configuration change.
>>>>>>
>>>>>> Kostya, what about moving to “tools” then?
>>>>>>
>>>>>
>>>>> Well, ok, this sounds cool.
>>>>> But can we make one more step and try to preserve the code
where it
>>>>> is, for the sake of compatibility?
>>>>>
>>>>>
>>>>> Please no. This code doesn't actually belong in lib, it
has never fit
>>>>> the model of an LLVM library, we really need to pull it out
of there.
>>>>>
>>>>> E.g. can we have the CMake in tools while still keeping the
code in
>>>>> lib?
>>>>>
>>>>>
>>>>> Could we contrive a hack in the build system to do it? Yes,
but I will
>>>>> fight violently against allowing that change into the build
system because
>>>>> the right answer here is to move the code.
>>>>>
>>>>> Or a link of some kind?
>>>>>
>>>>>
>>>>> Links are incredibly fragile on Windows, and they trip up a
lot of SCM
>>>>> tools. We have one in LLDB's repo that causes me
nothing but problems, so I
>>>>> am also strongly opposed to that.
>>>>>
>>>>>
>>>>> My worry is that there are already quite a few places that
know where
>>>>> libFuzzer code is,
>>>>> and I don't control all of them.
>>>>>
>>>>>
>>>>> Downstream clients will have to update. That is kinda how
these things
>>>>> work, I can't imagine re-pointing an SCM checkout being
a huge burden.
>>>>>
>>>>>
>>>>> And, finally, I really don't get why we can do
something in tools and
>>>>> can't do the same in lib.
>>>>> Or we simply don't want to do it to keep things simple?
>>>>>
>>>>>
>>>>> Not all functionality in CMake is order-independent.
Specifically the
>>>>> detection of targets is not. In order to support what
you're trying to do
>>>>> you are going to change behavior based on the presence of
the clang target.
>>>>> Which means the clang target must be added before your
CMake is processed.
>>>>>
>>>>> To support this our build system has strict ordering
requirements such
>>>>> that things in lib cannot depend on things in tools. If you
need to depend
>>>>> on clang, you need to not be in lib.
>>>>>
>>>>> Also, generally speaking Fuzzer is a library under lib that
also has
>>>>> nested tests, which is *not* how the lib directory is
supposed to be
>>>>> structured. It never should have been allowed to be
structured like that.
>>>>> If you want the tests next to the library, it is a tool or
a runtime, but
>>>>> not a lib.
>>>>>
>>>>> As I see there are two options to move forward with, and it
really
>>>>> depends on how you intend to use the just-built clang.
>>>>>
>>>>> (1) If you want to use just-built clang to build libFuzzer
and its
>>>>> tests, it should be a runtime.
>>>>> (2) If you want to use just-built clang to only build
libFuzzer's
>>>>> tests, it should be a tool.
>>>>>
>>>>> I think that since it is a runtime library, it should be a
runtime,
>>>>> and I expect it would mostly work to just copy the Fuzzer
directory into
>>>>> llvm/runtimes.
>>>>>
>>>>> -Chris
>>>>>
>>>>>
>>>>> --kcc
>>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> On May 9, 2017, at 11:07 AM, Dan Liew <dan at
su-root.co.uk> wrote:
>>>>>>
>>>>>> On 9 May 2017 at 18:55, Kostya Serebryany <kcc at
google.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, May 9, 2017 at 10:23 AM, Dan Liew <dan at
su-root.co.uk> wrote:
>>>>>>
>>>>>>
>>>>>> Does anyone see good reasons why libFuzzer should
remain in llvm repo
>>>>>> (as
>>>>>> opposed to moving it to compiler-rt)?
>>>>>>
>>>>>>
>>>>>> Does moving LibFuzzer to compiler-rt imply that it is
compiled as part
>>>>>> of compiler-rt and shipped with it?
>>>>>>
>>>>>> How does that fit with LibFuzzer's model of
allowing the user to
>>>>>> provide their own `main()`.
>>>>>>
>>>>>>
>>>>>>
>>>>>> libFuzzer doesn't allow users to use their own main
(not any more).
>>>>>> Although I am not sure how that's related to moving
libFuzzer
>>>>>> somewhere.
>>>>>>
>>>>>>
>>>>>> Oops. That shows how long it's been since I looked
at the source code.
>>>>>>
>>>>>> It was related in that if LibFuzzer was shipped as part
of compiler-rt
>>>>>> I presumed we would need to supply both libraries to
end users.
>>>>>> Given that this feature was removed it is a non-issue.
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
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